EXTRACTION OF IRON AND ALUMINIUM FROM RHEIR ORES

Question 1

Why is the extraction of Metals an important part of our everyday life?

Answer 1

Well, many useful metals such as Magnesium, Sodium, and Aluminum do not exist in their pure form naturally, they exist as ores, and as such they have to be extracted using various methods. Whenever they are extracted we are now able to utilize them in various ways to improve our lives. An example is the extraction of Aluminum from bauxite, one of its ores. When we extract the pure metal we are able to make cars, windows and other important things we use everyday.

Question 2

What is an ore? Explain fully.

Answer 2

An ore is a solid rock that is made up of or contains a metal in its combined state. The metal exists as a positive ion( cation). They are very often metal oxides.

Question 3

Name the apparatus used for the extraction of iron and how it received its name or rather what step in the process allows it to be called what it is called?

Answer 3

Blast Furnace.
Step 2 is the reason why this is called a blast furnace. Step 3 is the reason because hot air blasted through the bottom of the furnace

Question 4

Give 3 examples of an ore. State which element the ore contains.

Answer 4

Haematite- Iron
Magnetite-Iron
Bauxite- Aluminum

Question 5

What are the 4 reactions that take place int the process of extracting iron.

Answer 5

1. Combustion- (Carbon (burning with oxygen- at step 2)
2. Redox- (Carbon monoxide reducing or causing Iron to lose oxygen- at step 4)
3. Decomposition- (Thermal decomposition or the breaking down of the limestone, CaCO3, due to the high temperatures, into CaO and CO2- Step 5)
4. Neutralization- (The CaO is basic while the SiO2 is acidic hence they neutralize each other to produce Calcium Silicate CaSiO3- Step 5)

Question 6

Outline and explain the steps of extracting iron ensure to include balanced chemical equations in your answer.

Answer 6

1. A combined mixture called “the charge” is added to the top of the furnace. The charge includes:
   a. Iron ore, haematite- which often contains silicon dioxide (sand) with iron oxide.
   b. Limestone-CaCO3
   c. ‘Coke’ mainly contains carbon.
2. Hot air is blasted through the bottom of the furnace. The oxygen from the air reacts or burns with the carbon from the coke to produce carbon dioxide.
   This is an exothermic reaction. The heat released from the reaction keeps the bottom of the furnace at about 1900 degrees Celsius.
3. The carbon dioxide rises to the top of the furnace and further reacts with the coke to produce carbon monoxide.
4. The carbon monoxide produced from step 3 reacts with the iron oxide Fe2O3 reducing it to produce molten iron and Carbon dioxide.
5. The silicon dioxide that is present in the ore is an impurity hence the limestone is used to remove it in a two step process. Firstly due to the high temperature in the furnace, the CaCO3 is thermally decomposed to form CaO and CO2.

The CaO reacts with the SiO2 to form calcium silicate CaSiO3, known as slag.

The slag floats on top of the molten iron as it is lighter. Both the slag and molten iron are tapped of.

Question 7

Describe how the method for extracting metals is chosen.

Answer 7

The method is chosen mainly based on the metal’s position in the reactivity series.
For metals high up, they would require a method that gives high energy, namely electrolysis. The reason for this is because, they are so high up they are very reactive and as such they are strongly bonded within their ores, they form very stable ions as a result they are very hard to reduce in other words it is very hard for the metal to be broken from its oxygen, hence a lot of energy is required, energy that can only be effectively produced through electrolysis. Additionally, it needs a powerful reduction method. Potassium to Aluminum

For metals in the middle or generally Zinc and below, they are not as reactive and so they do not require a lot of energy, in fact, they are much easier to reduce and so they can be reduced or extracted by heating the ore with a reducing agent, whether carbon monoxide or carbon. For some metals such as silver and gold mostly occur in nature in their pure forms so they may not require any form of extraction, however, when they do exist in ores heating it is often strong enough to displace the metal

Question 8

Describe in detail the extraction of Aluminum from its ore.

Answer 8

Firstly, it is important to mention the fact that bauxite is the main ore from which Aluminum is extracted. Bauxite is impure hydrated Aluminum Oxide. This is purified using the Bayers Process where crushed bauxite is treated with moderately conc. NaOH which produces a white powdery substance called alumina.

The electrolysis of the aluminum oxide takes place in a large tank called a steel cell, where the walls are coated with carbon to act as the negative cathode, in the middle large blocks of graphite are hung in molten cryolite with the alumina to act as the positive anode.

At the cathode:
The aluminum 3+ ions move to the cathode where it is reduced by gaining 3 electrons to form Aluminum atoms. The molten aluminum is deposited to the bottom of the tank where the aluminum is tapped off periodically to make blocks or sheets.

At the anode:

The oxide ion moves to the anode where it is oxidized by losing electrons to produce oxygen. The oxygen exists as hot bubbles which react with the graphite anode to produce carbon dioxide. Over time the oxygen causes the anodes to “burn away” or disintegrate causing them to be replaced every 28 days or so.

The overall reaction of the electrolysis is:

2Al2O3(l) ——–> 4Al(l)+2O2(g)

Question 9

What are the two uses of cryolite?

Answer 9

1. To reduce the melting point of the alumina from 20240 degrees to 950 degrees Celsius.

Question 10

What happens to the graphite anodes after a time.

Answer 10

They burn away due to the oxygen and need to be replaced.